DIPHTHONGS
Certain words in our language require a linking or fusion of vowel sounds for pronunciation. Such combinations are known as diphthongs or compound vowels. To form them the articulatory organs move from one vowel position to another without making any articulatory break. Therefore the result is a continuous ±r,liding tone. Illustrations of words in which compound vowels occur are: house, now, aisle, my, mine, boy, oil, view, news, feud, tune, beauty. In the diphthong in house, the vowels ah and oo (as in look) are the sounds heard most prominently; in aisle, ah and i (as in it) are linked; in oil, aw (as in awl) and i (as in it) are pronounced; and in view, the vowel chamber is shaped for i (as in it) and then changed to 00 (as in too). Sometimes the sounds oh (as in go) and ay (as in say) are considered diphthongs. This is so especially in words like go, no, snow, pay, day, way, where the vowel is long. In oh the sound tends to become oo (as in look) while in ay it approximates i (as in it).
Vowels forming diphthongs do not receive equal stress. In ou (in house), ai (in aisle), of (in oil), oh (in go), and ay (in say) the first element is the more prominent. In iew (in view) the reverse is true. The difference in stress or emphasis, although true in both speech and song, is not so apparent in speech where the rate of utterance is more rapid. Because of the sustained quality in song, it is particularly important that the singer prolong the main element of the diphthong and pronounce the unstressed vowel lightly and quickly. It is also essential that each vowel be produced correctly and that the change from one sound to another be made smoothly and skillfully.